Two stocks are available. The corresponding expected rates of return are $\bar{r}_{1}$ and $\bar{r}_{2}$; the corresponding variances and covariances are $\sigma_{1}^{2}, \sigma_{2}^{2}$. and $\sigma_{12}$. What percentages of total investment should be invested in each of the two stocks to minimize the total variance of the rate of return of the resulting portfolio? What is the mean rate of return of this portfolio?